In an excerpt from his new book, Zayn, the 23-year-old One Direction alum says seeing pictures from 2014 makes him realize “how ill” he was, reports BBC News.

“Something I’ve never talked about in public before, but which I have come to terms with since leaving the band, is that I was suffering from an eating disorder,” he writes. “It wasn’t as though I had any concerns about my weight or anything like that.”

“I’d just go for days – sometimes two or three days straight — without eating anything at all,” he continues. “It got quite serious, although at the time I didn’t recognize it for what it was.”

The singer quit One Direction in March 2015, after missing a number of appearances with the rest of the band due to stress. Since then he has launched his own solo career and released his first album Mind of Mine last March and is currently dating model Gigi Hadid.

“I think [my eating disorder] was about control. I didn’t feel like I had control over anything else in my life, but food was something I could control, so I did,” he writes. “The workload and the pace of life on the road put together with the pressures and strains of everything going on within the band had badly affected my eating habits.”

Zayn also describes how anxiety has forced him to cancel big solo gigs.

“The idea of it totally freaked me out and I was paralyzed with anxiety,” he explains. “The plan is to start performing smaller venues and work my way up from there. This anxiety isn’t going to get the better of me.”